I'm having the same problem.
When I boot into the non-smp kernel the 6111 drivers work great, much better than the nv drivers. But when I switch to the SMP kernel X gets really confused and will sometimes run (sans all the twinview options I've setup) but crash a lot of programs (sorry no list right now), and other times it will just flicker and scroll like the refresh rate is off, definitely a driver issue. I'd say this driver version is just not SMP safe.
Thanks for the work nvidia, now opensource those drivers! Oh, and make them SMP safe please
Dual 2200+ athlon MP's
NV18 Quadro4 280 NVS
Mandrake 10 using the stock 2.6.3-7mdk and 2.6.3-7mdksmp kernels
The 2.6.3-7mdk kernel is supposedly supported, and yes, I did reinstall the driver after switching kernels. It could possibly be an issue with the detection scheme.